The invention herein described relates generally to systems and methods for measuring the volume of a liquid in a container. More specifically, the invention relates to systems and methods for determining the volume of fuel in an irregularly-shaped aircraft fuel tank.
The problem of measuring the volume of fuel in an aircraft fuel tank is complicated by two factors. First, such tanks generally have irregular shapes. Second, the orientation of an aircraft fuel tank is not fixed, since the aircraft changes its orientation during flight maneuvers.
Typically, fuel volume in an aircraft fuel tank is determined by use of look-up tables. For a given orientation of the aircraft and a measurement of the fuel level within the tank, a look-up table provides the volume of fuel in the tank. Such look-up tables are laborious to compile, since measurements of the fuel level within the tank must be made for a wide variety of orientations and known fuel volumes. Moreover, use of such look-up tables requires interpolation between the values of the fuel level and of the orientation for which the volume of fuel is known.
In addition, a change of tank design resulting in a change of shape generally requires the entire process of creating a look-up table to be repeated.
From the foregoing, it is clear that there is a need for a method of determining the volume of a liquid such as a fuel within an irregularly-shaped container of varying orientation, which can be accomplished without the expense and time required to generate and use look-up tables.
A volume measurement system according to the invention uses volume element counting in determining the amount of a liquid such as fuel in an irregularly-shaped container such as a fuel tank which can have changing orientation, as may arise from the fuel tank being located in an aircraft. In a preferred embodiment, the container is conceptually divided up into a plurality of volume elements. An orientation sensor determines the orientation of the container or of the liquid surface, which is approximated as a plane. A computational or optical processor uses orientation data to project vectors representing the volume elements onto a direction normal to the liquid interface plane. These projected distances are then arithmetically or optically compared to the location of the liquid interface plane.
According to one aspect of the invention, a liquid volume measurement system includes an orientation sensor to sense an orientation of a liquid surface within a container; a liquid level sensor to sense a level of the liquid surface; and a processor operatively coupled to the to the orientation sensor for receiving orientation data, and operatively coupled to the liquid level sensor for receiving the level. For each of a plurality of volume elements of the container, the processor compares an indication of a volume element location of the respective element with an indication of a surface location of the liquid surface.
According to another aspect of the invention, a method for measuring liquid volume, includes the steps of conceptually dividing a container into a plurality of volume elements; representing each of the volume elements by an associated point within the respective element, wherein for each of the volume elements there exists an associated vector between a fixed point and the respective associated point; determining a vector normal to a liquid surface within the container; determining a liquid surface distance between the fixed point and the liquid surface in the direction of the normal vector; projecting the associated vectors in the direction of the normal vector to determine a projected distance for each of the volume elements; and comparing each of the projected distances with the liquid surface distance.
According to a further aspect of the invention, a fuel volume measurement system includes an orientation sensor to sense an orientation of a fuel surface within a fuel tank; a fuel level sensor to sense a level of the fuel surface; and a processor operatively coupled to the to the orientation sensor for receiving orientation data, and operatively coupled to the fuel level sensor for receiving the level; a storage device operatively coupled to the processor, the storage device storing location data for each of a plurality of volume elements. For each of the volume elements of the fuel tank, the processor compares an indication of a volume element distance of the respective element along an axis normal to the fuel surface with an indication of a level distance of the surface along the axis, and wherein the processor further counts the volume elements having volume element distances less than the level distance and divides the count by the number of the volume elements.
According to a still further aspect of the invention, a method of determining the dielectric constant of a liquid includes the steps of: determining an orientation of a container containing at least some of the liquid; and calculating the dielectric constant of the liquid using capacitance readings from each of two or more partially-covered capacitance probes in the container, the orientation of the container, location data of the probes, and the operating characteristics of the probes.
According to yet another aspect of the invention, a system for determining the projection of one or more vectors in a direction includes a vector optical element which has one or more areas, each area being an optical analog of at least part of one of the one or more vectors; and a direction optical element optically coupled to the vector optical element, the direction element being an optical analog of the direction.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.